I'm trying to figure out programming with GLSL and I'm slightly confused on what I'm supposed to do. I've figured out how to pass a vertex array, an array of texture coordinates (per vertex), an element array and two textures to a simple GLSL program. I'm using pygame for the simplicity while I'm learning.
I create vertices, texture coordinates and an element array like this:
w = 16
h = 12
vertex_array = []
tex_coord_array = []
element_array = []
for i in range(h):
for j in range(w):
vertex_array += [-1.0+j*2.0/(w-1), 1.0-i*2.0/(h-1), 0.0, 1.0]
if j%2:
tex_coord_array += [1.0]
else:
tex_coord_array += [0.0]
if i%2:
tex_coord_array += [0.0]
else:
tex_coord_array += [1.0]
for i in range(1,h):
for j in range(1,w):
element_array += [(i-1)*w+(j-1), i*w+(j-1), (i-1)*w+j]
element_array += [i*w+(j-1), i*w+j, (i-1)*w+j]
... giving me a simple "wall" of textured triangles using the following shaders:
vertex_shader = '''\
#version 110
attribute vec2 tex_coord;
attribute vec4 position;
varying vec2 texcoord;
void main()
{
gl_Position = position;
texcoord = tex_coord;
}
'''
and
fragment_shader = '''\
#version 110
uniform sampler2D textures[2];
varying vec2 texcoord;
void main()
{
gl_FragColor = texture2D(textures[0], texcoord);
}
'''
Right now I get the texture mirroring in every direction (on every 4 quads) since I only supply one texture coord per vertex instead of passing one per element of the element array. I want to have all quads textured with the correct aligned texture (since I told myself that was a good start in GLSL ^^), what would be the way to do this?
Thanks!
UPDATE:
As Nicol Bolas pointed out - this isn't really a GLSL problem. For now I've just redone the vertex/coord/element generation to this:
for i in range(h):
for j in range(w):
# first triangle
vertex_array += [-1.0+j*2.0/(w-1), 1.0-i*2.0/(h-1), 0.0, 1.0]
tex_coord_array += [0.0, 1.0]
vertex_array += [-1.0+j*2.0/(w-1), 1.0-(i+1)*2.0/(h-1), 0.0, 1.0]
tex_coord_array += [0.0, 0.0]
vertex_array += [-1.0+(j+1)*2.0/(w-1), 1.0-i*2.0/(h-1), 0.0, 1.0]
tex_coord_array += [1.0, 1.0]
# second triangle
vertex_array += [-1.0+j*2.0/(w-1), 1.0-(i+1)*2.0/(h-1), 0.0, 1.0]
tex_coord_array += [0.0, 0.0]
vertex_array += [-1.0+(j+1)*2.0/(w-1), 1.0-(i+1)*2.0/(h-1), 0.0, 1.0]
tex_coord_array += [1.0, 0.0]
vertex_array += [-1.0+(j+1)*2.0/(w-1), 1.0-i*2.0/(h-1), 0.0, 1.0]
tex_coord_array += [1.0, 1.0]
element_array = range(h*w*6)
And it works - but it feels sort of wasteful to use six times as many vertices just to get the texture coordinates right...
